全文获取类型
收费全文 | 32628篇 |
免费 | 200篇 |
国内免费 | 293篇 |
专业分类
化学 | 12870篇 |
晶体学 | 296篇 |
力学 | 1451篇 |
综合类 | 12篇 |
数学 | 9752篇 |
物理学 | 8740篇 |
出版年
2023年 | 45篇 |
2022年 | 105篇 |
2021年 | 144篇 |
2020年 | 117篇 |
2019年 | 131篇 |
2018年 | 1311篇 |
2017年 | 1546篇 |
2016年 | 847篇 |
2015年 | 659篇 |
2014年 | 579篇 |
2013年 | 896篇 |
2012年 | 3308篇 |
2011年 | 2558篇 |
2010年 | 1968篇 |
2009年 | 1700篇 |
2008年 | 763篇 |
2007年 | 800篇 |
2006年 | 783篇 |
2005年 | 4603篇 |
2004年 | 4045篇 |
2003年 | 2405篇 |
2002年 | 576篇 |
2001年 | 347篇 |
2000年 | 138篇 |
1999年 | 208篇 |
1998年 | 143篇 |
1997年 | 98篇 |
1996年 | 69篇 |
1995年 | 62篇 |
1994年 | 66篇 |
1993年 | 52篇 |
1992年 | 187篇 |
1991年 | 184篇 |
1990年 | 151篇 |
1989年 | 120篇 |
1988年 | 107篇 |
1987年 | 71篇 |
1986年 | 61篇 |
1985年 | 58篇 |
1984年 | 58篇 |
1983年 | 46篇 |
1981年 | 46篇 |
1979年 | 54篇 |
1978年 | 51篇 |
1977年 | 45篇 |
1976年 | 91篇 |
1975年 | 57篇 |
1974年 | 56篇 |
1973年 | 58篇 |
1972年 | 46篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
Ivan Kojadinovic 《4OR: A Quarterly Journal of Operations Research》2007,5(2):117-142
The application of multi-attribute utility theory based on the Choquet integral requires the prior identification of a capacity
if the utility scale is unipolar, or of a bi-capacity if the utility scale is bipolar. In order to implement a minimum distance
principle for capacity or bi-capacity approximation or identification, quadratic distances between capacities and bi-capacities
are studied. The proposed approach, consisting in solving a strictly convex quadratic program, has been implemented within
the GNU R kappalab package for capacity and nonadditive integral manipulation. Its application is illustrated on two examples.
相似文献
33.
Piotr Ko?cielniak 《Topology and its Applications》2007,154(9):1951-1955
Let M be a compact manifold with dimM?2. We prove that some iteration of the generic homeomorphism on M is semiconjugated to the shift map and has infinite topological entropy (Theorem 1.1). 相似文献
34.
Covering numbers of precompact symmetric convex subsets of Hilbert spaces are investigated. Lower bounds are derived for sets containing orthogonal subsets with norms of their elements converging to zero sufficiently slowly. When these sets are convex hulls of sets with power-type covering numbers, the bounds are tight. The arguments exploit properties of generalized Hadamard matrices. The results are illustrated by examples from machine learning, neurocomputing, and nonlinear approximation. 相似文献
35.
We give counterexamples to the following conjecture of Auslander: given a finitely generated module M over an Artin algebra Λ, there exists a positive integer nM such that for all finitely generated Λ-modules N, if ExtΛi(M,N)=0 for all i?0, then ExtΛi(M,N)=0 for all i?nM. Some of our examples moreover yield homologically defined classes of commutative local rings strictly between the class of local complete intersections and the class of local Gorenstein rings. 相似文献
36.
Andrew Mills Anne Lepre Nicholas Elliott Sharan Bhopal Ivan P. Parkin S. A. ONeill 《Journal of photochemistry and photobiology. A, Chemistry》2003,160(3):213-224
Pilkington Glass Activ™ represents a possible suitable successor to P25 TiO2, especially as a benchmark photocatalyst film for comparing other photocatalyst or PSH self-cleaning films. Activ™ is a glass product with a clear, colourless, effectively invisible, photocatalytic coating of titania that also exhibits PSH. Although not as active as a film of P25 TiO2, Activ™ vastly superior mechanical stability, very reproducible activity and widespread commercial availability makes it highly attractive as a reference photocatalytic film. The photocatalytic and photo-induced superhydrophilitic (PSH) properties of Activ™ are studied in some detail and the results reported. Thus, the kinetics of stearic acid destruction (a 104 electron process) are zero order over the stearic acid range 4–129 monolayers and exhibit formal quantum efficiencies (FQE) of 0.7×10−5 and 10.2×10−5 molecules per photon when irradiated with light of 365±20 and 254 nm, respectively; the latter appears also to be the quantum yield for Activ™ at 254 nm. The kinetics of stearic acid destruction exhibit Langmuir–Hinshelwood-like saturation type kinetics as a function of oxygen partial pressure, with no destruction occurring in the absence of oxygen and the rate of destruction appearing the same in air and oxygen atmospheres. Further kinetic work revealed a Langmuir adsorption type constant for oxygen of 0.45±0.16 kPa−1 and an activation energy of 19±1 kJ mol−1. A study of the PSH properties of Activ™ reveals a high water contact angle (67°) before ultra-bandgap irradiation reduced to 0° after prolonged irradiation. The kinetics of PSH are similar to those reported by others for sol–gel films using a low level of UV light. The kinetics of contact angle recovery in the dark appear monophasic and different to the biphasic kinetics reported recently by others for sol–gel films [J. Phys. Chem. B 107 (2003) 1028]. Overall, Activ™ appears a very suitable reference material for semiconductor film photocatalysis. 相似文献
37.
It can be conjectured that the colored Jones function of a knot can be computed in terms of counting paths on the graph of
a planar projection of a knot. On the combinatorial level, the colored Jones function can be replaced by its weight system.
We give two curious formulas for the weight system of a colored Jones function: one in terms of the permanent of a matrix
associated to a chord diagram, and another in terms of counting paths of intersecting chords.
Electronic supplementary material to this article is available at and is accessible to authorized users.
* S. G. was partially supported by an NSF and by an Israel-US BSF grant.
† M. L. was partly supported by GAUK 158 grant and by the Project LN00A056 of the Czech Ministry of Education. 相似文献
38.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth
domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated
on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used
to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in
the case where the principal part of the differential operator is the Laplacian.
Online publication 23 January 2004. 相似文献
39.
40.
Anelia Achanova Ivan Zhelyazkov Tsvetelina Petrova 《Czechoslovak Journal of Physics》2004,54(2):211-223
Microwave discharges produced by travelling/standing electromagnetic waves have drawn considerable attention in recent years
due to their wide application in microelectronic industry. Here are presented the axial distributions of the electrons and
ions as well as those of excited atoms in an argon microwave discharge at a low gas pressure (400 mTorr) sustained by a 2.45
GHz travelling dipolar electromagnetic wave. The numerical calculations are based on a self-consistent kinetic-electrodynamic
model and the results obtained are in a good agreement with the experimental data. The model yields also the magnitude of
the wave power sustaining the discharge and the axial profiles of all electromagnetic-wave characteristics and the axial distribution
of the neutral gas temperature. 相似文献